An extruder head is known which is used to make complex parts of different resins. Such a head is connected to a plurality of extruders and has head parts each forming a passage having an upstream end connected to a respective one of the extruders and a downstream end opening at a die. The various resins are forced at very great pressure, often in excess of 500 bar, along the respective passages to merge at the die and form a workpiece of the desired shape.
It is necessary to be able to open up such a head assembly, for servicing and cleaning and for changing the die. Accordingly German patent 4,234,280 of Kaufmann and US Pat. No. 4,824,353 and 5,851,561 both of Hirschkorn propose systems where the head parts are pivoted on a stationary mold part so that they can be moved between positions where their downstream passage ends merge at the die and positions with their downstream ends separated and the passages exposed.
Such system are all very bulky and difficult to maintain tightly together under the enormous working pressures of the extrusion apparatus. Accordingly hydraulic locks are provided which clamp the head parts to the stationary head part. Such locks normally are constituted as hydraulic cylinders carried on the stationary part and having piston rods that engage formations of the respective head parts to pull same solidly together and against the stationary part.
While these arrangements are relatively effective, they do not completely rule out shifting of the head parts and, therefore, leakage from between the movable parts of the extruder head. The cylinders must exert considerable clamping force in order to hold the interfaces between the head parts together even though they usually are able to effectively prevent leakage between the head parts and the actual mold.